The present invention relates to mechanisms for venting gases from fluid systems, and, more particularly, to mechanisms for venting air from the hydraulic systems of aircraft and the like.
It is well known that air tends to become entrained or dissolved in liquids such as the oil of hydraulic systems. Admitted through imperfect seals, for the most part, the air can form pockets at quiet spots in the system leading to possible pump cavitation and adversely affecting the heat conductivity, bulk modulus, oxidation resistance and other physical properties of the oil. It is, therefore, desirable to degas the oil, preferably on a continuous or cyclic basis, whenever the system is in use.
Degassing is a particularly difficult problem in an aircraft hydraulic system where size and weight limitations are severe, reliability is critical and the apparatus will sometimes be inverted and subjected to abrupt changes in altitude. A particularly advantagous degassing device suitable for use in aircraft is described in U.S. Pat. No. 3,969,092, entitled LIQUID DEGASSING DEVICE, issued to John A. Huffman and Vincent G. Magorien on July 13, 1976. While this degasser has proven highly effective, there is a desire for functional improvement in several respects.
It has been found to be difficult for maintenance personnel to determine whether a degasser is operating properly since the amount of air expelled is too small to be heard or felt. If verification of venting activity is desired, it is necessary to temporarily connect the degasser to a bubbler in which the passage of vented air through a fluid can be observed. This is an inconvenient and time consuming procedure since an aircraft degasser is often inaccessible.
In addition to the concern of aircraft designers that a degasser may cease to function effectively without the problem being detected, there is also a related concern that the degasser may fail in such a manner that oil will be allowed to escape with a resulting loss of pressure throughout the hydraulic system. Although the above-mentioned degasser contains a provision for preventing the escape of oil, there is no convenient testing procedure for determining whether the device is capable of operating properly in this emergency situation.
Accordingly, there is a need for an air venting mechanism that provides verification of the fact that air is being vented and prevents liquid from passing out of the system through the degasser. It is desirable that such a mechanism includes a provision for easily and conveniently testing its continued ability to perform this shut-off function and is not adversely affected or disabled by repeated inversions, changes in altitude and changes in ambient pressure. The present invention fills the foregoing needs.